Effect of Chromatin modification on meiosis:wheat, a model for polyploid crops

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Most related chromosomes of wild relatives of wheat exhibit extensive gene synteny along their chromosome length. Moreover the genes on related chromosomes exhibit more than 95% homology at the sequence level. Despite this level of similarity, there is little recombination between wild relative and wheat chromosomes at meiosis due the presence of the Ph1 locus. The wild relative chromosomes and wheat chromosomes differ in their repetitive content and the level of transcription from their genes. Deletion of the Ph1 locus allows the chromosomes to behave like homologous chromosomes and recombine. Recombination involves the initiation of double strand breaks within genic regions and then repair of breaks. Recent data indicates that Ph1 is affecting chromatin structure and this affects the distribution and processing of double strand breaks. Thus Ph1 is affecting the genic regions in some way enabling them to be recognised, or not, in terms of the recombinational machinery.

By exploiting next generation sequencing and cell biological approaches, we will identify what is being altered in the genic regions by the presence or absence of Ph1 at the onset of meiosis. We will access whether there is altered distribution of double strand breaks or their processing, chromatin structure or methylation of and transcription from the genic regions. From this information, we will treat developing wheat anthers prior to meiosis with drugs which themselves induce similar changes and then score the resulting effects on chromosome pairing during metaphase I, to confirm the association of the particular change with a pairing effect.

In the past there are examples where the wild relatives of wheat have been successfully exploited as a novel source of genetic variation for traits in wheat breeding programmes. However, the introgression of genes from wild relatives into wheat is very time consuming and inefficient and therefore fell out of favour. Recently, international breeding centres have again started to exploit wheat's wild progenitors, to generate synthetic hexaploid Triticum aestivum, in order to create a "synthetic wheat" breeding programme. Some 25% of elite lines of wheat generated by CIMMYT are derived from crosses to these synthetic wheat genotypes. Having exploited this approach successfully, many now argue that to increase yield production in wheat it is imperative to revisit the exploitation of genetic variation available in the wild relatives in breeding programmes. As a result of this, a number of private sector breeders are encouraging the reestablishment of wheat alien introgression in the UK public sector.

To facilitate the transfer of genetic variation via wheat/alien introgression, research is required to increase the speed and enhance the efficiency of the process. In brief, wheat/alien introgression involves the hybridisation of wheat with a wild relative followed by repeated backcrossing to generate lines of wheat carrying an alien chromosome on which a target gene is located. A series of further crosses to specific genotypes/mutant lines are then required before the chromosome of the alien species can recombine within those of wheat, allowing the transfer of the target gene to wheat without linked deleterious effects.

There are some key barriers to the exploitation of wild species in breeding programmes. These barriers include the ability to make the initial hybrid and the time taken to induce exchange between chromosomes of wheat and the wild species. The advent of novel approaches for tackling these problems now means that a wheat/alien introgression programme can, once more, be considered.


The expected outcome of this project will the creation of tools to allow breeders to have access to the genetic potential of wild wheat species that possess non-collinear chromosomes and which cannot normally be introgressed into wheat. It will also allow the development of a skills base, which can be utilised by the next generation of scientists involved in wheat breeding and the larger wheat breeding community.